In recent years, as display devices of personal computers, televisions, cellular phones and the like, a large number of displays utilizing liquid crystal are used. In these liquid crystal displays, a surface light source called backlight is provided to irradiate light from the backside, thereby allowing images to be displayed. In order to comply with the demand that the entire screen must be uniformly irradiated, such backlight has a structure of a surface light source referred to as “edge-type” or “direct-type”. Among such backlights, for those thin liquid crystal displays used in notebook computers and the like that are desired to be made thin and small, an edge-type backlight, that is, a type of backlight in which a light source is arranged laterally with respect to the screen is applied.
In this edge-type backlight, a cold cathode fluorescent lamp or LED is used as a light source and light is uniformly propagated and diffused from the edge of a light guide plate to uniformly irradiate the entire liquid crystal display. In addition, in order to utilize light more efficiently, a reflection plate is provided around the light source and in order to allow the light diffused from the light guide plate to be efficiently irradiated to the side of the liquid crystal display, a reflection plate is also provided in the back of the light guide plate. By this constitution, the loss of the light emitted from the light source is reduced and a function to brightly illuminate the liquid crystal display is imparted.
Meanwhile, in those backlights for big screens used in liquid crystal display televisions, in addition to the edge-light system, a direct-type light system is employed. In this system, cold cathode fluorescent lamps are arranged in parallel on the backside of liquid crystal panel and a reflection plate is further arranged in the back of the cold cathode fluorescent lamps. By this constitution, the light emitted from the light source is effectively irradiated to the side of the liquid crystal display.
In such reflection plates used in a backlight for liquid crystal displays, as cellular phones and notebook computers are made thinner and smaller and televisions are made bigger, there is an increasing demand for a reflection plate which, despite being thin, has excellent reflective properties, excellent light-concealing properties and high rigidity.
Conventionally, in reflection plates, a constitution which utilizes light reflection produced by the differences in the refractive index at the interfaces between minute voids and matrix resin contained in a film is widely employed (see Patent Document 1). In order to achieve superior reflective properties, the shape and number of the voids are critical, and there is a reflection plate in which these properties are controlled (see Patent Documents 2 to 6).